With the rapid development of highways and the automotive logistics industry in China, the quantity of commercial vehicles/passenger cars is becoming more and more. After a rolling bearing and a wheel hub body of a vehicle are assembled to an axle, a bearing outer ring rotates relative to a wheel axle, but a bearing inner ring cannot rotate relative to the wheel axle. The bearing inner ring is only stressed at a bottom portion (accounting for about ⅕ to ⅓ of the entire circumference), thereby suffering concentrated stress, and the wear degree of an outer ring in each work cycle, namely works for a circumference, only corresponds to the wear degree of the bottom portion of an inner ring, the service lives of the two components are “seriously unequal”. A linear perimeter of the inner ring raceway of the rolling bearing is smaller than that of the outer ring raceway of the bearing, resulting in that the relative linear velocity of the bearing inner ring and a bearing rolling body is much higher than that of the bearing outer ring. When the vehicle is running smoothly, the bearing normally operates, and the rolling body is in a “capable of rolling” state; and when the vehicle is driving on an uneven road, a momentary “incapable of rolling” state of the rolling body will be generated, the rolling body slides in the inner ring raceway, generating a high temperature, “fatigue pitting” of the bearing inner ring starts, and agglutination and ablation of the inner ring raceway of the bearing will be produced after multiple continuous repeated processes, which finally results in the invalidity of the rolling bearing.
In addition, the wheel hub body and the rolling bearing and other parts of the wheel hub unit are provided by manufactures in the form of separated part, which are assembled together by the wheel hub unit supplier, so the assembly efficiency is low, and a problem that the bearing inner rings are exchanged and assembled in a mixed way is generated easily in an assembly process of the two rolling bearings, thereby influencing the assembly precision and the service life of the bearings. Furthermore, the bearing inner ring of the existing wheel hub unit is directly matched with the wheel axle, so the sealing property cannot be guaranteed, particularly: there is a leakage problem of the lubricating substances between the bearing outer ring and the wheel hub body and between the bearing inner ring and the wheel axle. Moreover, a stress generated by a spindle head nut used for adjusting a bearing clearance after pre-tightening directly and consistently acts on the bearing inner ring, resulting in the deformation of the raceway during use, and thus the service life of the rolling bearing is greatly shortened.